Clad materials obtained by bonding a plurality of metals through rolling are integrated materials that preserve the characteristics of individual, metals, and are hence extremely useful in applications in which a plurality of characteristics must be provided at the same time.
For example, cases for button-type microbatteries must have the desired mechanical strength, drawability, corrosion resistance, low contact resistance, and the like. CU/SUS (stainless steel)/Ni, Cu/Fe/Ni, and other clad materials are used for anode cases; and Ni/SUS, Ni/SUS/Ni, Al/SUS/Ni, and other clad materials are used for cathode cases.
In addition, Ni/Fe/Ni, Ni/SUS/Ni, Cu/SUS/Ni, Cu/Fe/Ni, and other clad materials are used for the cases of various electronic components that have specific requirements concerning mechanical strength, drawability, corrosion resistance, weldability, and the like.
Clad materials that function as base materials for such cases are commonly obtained by superposing a plurality of metal sheets constituting a clad material, bonding these sheets by cold rolling, homogenizing the sheets, and subjecting them to finish cold rolling or a combination of finish cold rolling and final annealing. The product may be optionally cut into prescribed lengths.
Clad materials obtained by the aforementioned manufacturing method are molded into cup shapes by conventional deep drawing, making it possible to obtain cases designed for various applications and fashioned to specific dimensions.
For example, miniaturization of cases for the aforementioned button-type microbatteries becomes crucial because of the need for smaller and lighter devices in the field of electrical equipment.
Specifically, demand for thinner clad material increases because of the need to design cases for smaller button-type microbatteries that have higher capacity and longer life. Conventionally at about 0.2.about.0.3 mm, device thickness is currently being reduced to about 0.1.about.0.15 mm.
It has been confirmed that conventional manufacturing methods make it difficult to perform deep drawing as desired even when the goal is limited to obtaining a thin clad material. Specifically, the inventors have performed experiments and confirmed that an attempt to obtain a clad material by a conventional manufacturing method results in a high Lankford value, or a considerable difference between r values (which characterize the plastic anisotropy between the rolling/bonding direction and a direction at a prescribed angle to the rolling bonding direction). In addition, deep drawing produces low roundness and yields an oval shape whose major axis is oriented in the rolling/bonding direction. In particular, cracks and ruptures form and a cup shape is difficult to obtain when a thin clad material is formed.